1. Field of the Invention
This invention relates to improved catalysts for the dehydrogenation of hydrocarbons to corresponding more-unsaturated hydrocarbons, more particularly, to the production of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons and to the production of olefins from the corresponding more-saturated aliphatic hydrocarbons.
2. The Prior Art
The vinyl benzenes and butadienes play a particularly important role in the preparation of synthetic rubbers, plastics and resins. The polymerization of styrene for example with various co-monomers such as butadiene to produce synthetic rubbers is well known as is the polymerization of styrene to produce polystyrene resins.
Styrene and butadiene are typically produced from ethyl benzene and butylene, respectively, by dehydrogenation over solid catalysts in the presence of steam, and at temperatures ranging from 500.degree. C. to 700.degree. C. The class of catalysts found to be the most effective for this process is a potassium oxide (carbonate) promoted, chromium oxide stabilized, iron oxide material. Considerable research has gone into attempting to improve the activity and selectivity of this class of catalysts. Any improvement which results in either increasing the selectivity (moles of desired product produced per mole of reactant reacted) or the conversion (moles of reactant reacted per mole of starting material) without lowering the other is economically attractive since the result is that the yield (moles of desired product produced per mole of reactant) of the product has been increased. Any increase in the numerical value of the yield results in a more efficient operation with more reactant being converted into the desired product. In commercial operations, many of which produce millions of pounds of product per year, a trade-off is frequently effected between selectivity and conversion. An increase of only 1 or 2 percentage points in the selectivity can result in a substantial savings of starting materials. An increase in conversion can substantially reduce capital expenditure and energy consumption. The trade-off may vary depending on raw materials costs, energy costs, and the age of the plant.
The addition of vanadium pentoxide is known to improve the selectivity of the iron-chromium-potassium oxide catalysts. Such catalysts containing vanadium pentoxide were disclosed in U.S. Pat. No. 3,361,683 to W. R. Gutmann, issued Jan. 2, 1968, in U.S. Pat. No. 3,084,125 to F. J. Soderquist issued Apr. 2, 1963, or in Belgium Pat. No. 828,252, published Oct. 23, 1975.
Addition of cobalt to a typical iron-chromium-potassium oxide catalyst has been disclosed in U.S. Pat. No. 3,291,756 to R. S. Bowman, issued Dec. 13, 1966. Copending applications Ser. Nos. 740,272, now U.S. Pat. No. 4,052,338, and 740,264, now abandoned, filed Nov. 8, 1976 disclose the addition of small amounts of cobalt to iron-chromium-potassium-vanadium oxide catalysts. Copending Ser. No. 763,180 filed Jan. 27, 1977, now U.S. Pat. No. 4,098,723, discloses the addition of small amounts of cobalt to iron-potassium-vanadium oxide catalyst. U.S. Pat. No. 3,904,552 to O'Hara, issued Sept. 9, 1975, disclosed the use of cerium and molybdenum in dehydrogenation catalysts. Belgium Pat. No. 811,145 published June 17, 1974 disclosed the use of cerium in dehydrogenation catalysts. Belgium Pat. No. 811,191, published June 17, 1974 disclosed the use of cerium and molybdenum in dehydrogenation catalysts. U.S. Pat. No. 3,703,593 to Turley et al issued Nov. 21, 1972, disclosed the use of molybdenum as a promoter. U.S. Pat. No. 3,179,707 to Lee, issued Apr. 20, 1965, disclosed the use of vanadium, cobalt, cerium, and other metal in dehydrogenation catalysts. U.S. Pat. No. 3,505,422 issued Apr. 7, 1970 to Brewer et al and U.S. Pat. No. 3,424,808 issued Jan. 28, 1969 to Brewer et al disclosed the use of Group VIII metals, particularly cobalt, among others, in dehydrogenation catalysts. U.S. Pat. No. 3,223,743 issued Dec. 14, 1965 to Alistair disclosed the use of group IV to VIII metals particularly cerium in dehydrogenation catalysts. U.S. Pat. No. 2,603,610 to Amos et al, issued July 15, 1952; U.S. Pat. No. 2,414,585 to Eggertsen et al, issued Jan. 21, 1947; U.S. Pat. No. 2,460,811 to Davies et al, issued Feb. 8, 1949 and U.S. Pat. No. 2,461,147 to Davies et al, issued Feb. 8, 1949 are references that disclosed a number of metals used in dehydrogenation catalysts.